Optimized frequency comb spectrum of parametrically modulated bottle microresonators

Abstract

Optical frequency combs generated by parametric modulation of optical microresonators are usually described by lumped-parameter models, which do not account for the spatial distribution of the modulation. This study highlights the importance of this spatial distribution in the Surface Nanoscale Axial Photonics (SNAP) platform, specifically for elongated SNAP bottle microresonators with a shallow nanometre-scale effective radius variation along its axial length. SNAP bottle microresonators have much smaller free spectral range and may have no dispersion compared to microresonators with other shapes (e.g., spherical and toroidal), making them ideal for generating optical frequency combs with lower repetition rates. By modulating parabolic SNAP bottle microresonators resonantly and adiabatically, we show that the flatness and bandwidth of the optical frequency comb spectra can be enhanced by optimizing the spatial distribution of the parametric modulation. The optimal spatial distribution can be achieved experimentally using piezoelectric, radiation pressure, and electro-optical excitation of a SNAP bottle microresonator.